1. Field of the Invention
This invention relates to a process for the manufacture of olefinic polymers in the presence of a selected catalyst.
2. Prior Art
Catalyst compositions comprising zirconium compounds, typically metallocene and aluminoxane are known for use in the homopolymerization of olefins such as ethylene or the copolymerization of ethylene/alpha-olefins as disclosed for example in Japanese Laid-Open Patent Publication No. 58-19309. While the disclosed prior art process is advantageous so far as concerns the availability of polymerized products at increased rate of yield, it has a drawback in that the polymers obtained have a relatively narrow distribution-of molecular weight or composition, coupled with a relatively low molecular weight. When taking into account the molecular weight alone, it would be possible to increase the molecular weight of a polymer to some extent by making a proper selection of transition metals from among the group of metallocene. The molecular weight of a polymer may be increased by the use of a transition metal compound having a 2,3 and 4-substituted cyclopentadienyl group as disclosed in Japanese Laid-Open Patent Publication No. 63-234005, or by the use of a hafnium compound having a ligand bonded to at least two cross-linked conjugated cycloalkadienyl groups as disclosed in Japanese Laid-Open Patent Publication No. 2-22307. However, such catalyst components are complicated if not difficult to synthesize. The use of hafnium compounds is not very conducive to polymer yields. The prior catalysts being often soluble in the reaction system are further disadvantageous in that the polymer resulting from slurry or gas-phase polymerization would have reduced bulk density and deteriorated granular properties.